#include <iostream>
// 返回值优化，两个编译器都可以
struct C {
  C() {}
  C(const C&) { std::cout << "A copy was made.\n"; }
};

C f() {
  return C();
}

int main() {
  std::cout << "Hello World!\n";
  C obj = f();
    // 两者表示相同
  const int a = 0;
  int const b = 0;
  
  return 0;
}